The present invention relates to forming a plurality of flat, stiff articles such as flat-folded boxes flowing as a stream of overlapping shingled flat articles, into a stack, more particularly to a method and a device for automatically doing so as well as a device for counting the number of flat articles formed into the stack.
In the production of corrugated boxes, corrugated board produced at a corrugated machine is cut and converted into blanks of a desired shape, which are then may be printed or surface finished in some other way. Thereafter, the blanks are flat-folded and glued to form boxes, in a machine commonly known as a folder-gluer machine.
At the outlet of a folder-gluer machine, individual flat-folded and glued boxes are stacked in an overlapping shingled relationship, either in under-stacking or in top-stacking. Under-stacking means that there is a preceding box and a subsequent box, each with a leading edge and a trailing edge (seen in the direction of movement on a moving mechanism such as a conveyor belt), the preceding box being deposited on the moving mechanism before the subsequent box, and whereby the leading edge of the subsequent box is deposited on said moving mechanism under the trailing edge of said preceding box. Top-stacking means that there is a preceding box and a subsequent box, each with a leading edge and a trailing edge again, the preceding box being deposited on the moving mechanism before the subsequent box, whereby the leading edge of the subsequent box is deposited on the moving mechanism on top of the trailing edge of the preceding box.
This shingled flow is moved on between drying pressing belts to be pressed together well and to give sufficient glue drying time, in order to prevent unfolding of the boxes before their glue sets. After leaving the drying pressing belt, generally controlled packets, comprising one or more stacks made in a packeting machine from this flow of shingled individual boxes, are supplied to a strapping machine or strapping section, in order finally to be stacked neatly by a palletising station.
To achieve stable stacking on a pallet, the individual packets should have the same dimension and all opposing sides of the packets must be parallel with each other. Therefore the packeting machine should always make a stack having the same number of individual flat-folded boxes, should align these and where applicable compensate for any angled sides by placing another stack rotated through 180xc2x0 or another suitable angle (e.g. 90xc2x0) on the top, thus forming a packet. This block-like packet is then offered in a way ready positioned for the strapping machine.
In recent years suppliers of machines for handling corrugated cardboard have made significant innovations, especially in the field of folder-gluer machines, which have become considerably faster and more flexible in formats and types of boxes they can handle. The set-up time of such machines has become low and thus also allows profitability in small series. As always, the weakest link in the chain determines the profitability, and this weakest link is at present the packeting machine or packer installation which is still labour-intensive, and restricted in processing of box formats and types. Apparently, development of the subsequent machines (such as e.g. the packeting machine) has lagged behind despite the fact that investment already made for the folder-gluer machines would normally justify further optimisation of the line. These needs have led some machine manufacturers trying to fulfil demand. Unfortunately, known designs do not meet the range of products and format differences, the requirements due to the existing short set-up time, the restricted installation space and, last but not least, the price.
By increasing the production speed of the folder-gluer machines (to more than 15,000 boxes per hour), an extremely dynamic system is required for the packeting machine, to the extent that now the outer limit of present servo-technology is reached. The flexibility in product dimensions and forms further increases the degree of difficulty of forming packets from a continuously supplied stream of flat-folded boxes. The fact that under-stacking is now used more and more, and that the new folder-gluer machines allow this, means that a special approach is required for forming stacks out of the shingled flow, without neglecting the more traditional form of stacking, known as top-stacking.
Different mechanisms already used to separate individual flat-folded boxes to form a stack have been investigated:
1. Individual acceleration of boxes, which are then pushed under each other to form a stack, or which are dropped on top of each other, thus forming a stack.
2. Acceleration at the lower edge of some of the shingled boxes, which together will form a stack, and dropping them on top of each other one at a time in a catchment tray at a lower level.
3. Insertion of a separation finger in a stack where separation must occur and forward movement of a bridge, where the packet is located straight against an upright stop plate. An example of this has been described e.g. in U.S. Pat. No. 5,493,104.
4. Both accelerating the lower edge and the top edge of shingled boxes, and allowing the boxes to fall into a catchment tray below.
5. Obliquely stacked boxes are raised and allowed to fall individually into a catchment tray where they can fall further as a stack after being counted.
All of these solutions present the disadvantage that either the flat-folded boxes must be presented to the packeting machine on a one by one basis, or the continuous shingled flow has to be stopped, which solutions both slow down the handling.
Furthermore, corrugated cardboard boxes are not always rectangular in structure in a flat-folded state (e.g. locking bottom) and/or are not always glued symmetrically (e.g. an automatic-bottom box has, in flat-folded form, five thicknesses of cardboard where the bottom of the box lies, while it has only two thicknesses of cardboard where the top of the box lies). As a result, a number of boxes pushed onto each other in the same direction, forms a stack with the top side misaligned. Hence, when the boxes are stacked for handling or storage, the stack that is formed will have a tendency to topple if all packs of boxes are stacked in the same direction. To make such a stack into a block, it is known to rotate a second stack through 180xc2x0 in the vertical or horizontal plane. This is called compensation. Depending on the product form, the packet thus formed is more or less unstable (due to accordion movement).
To compensate for the stacks and eliminate misalignment due to oblique sides, various mechanisms are known.
1. A stack of boxes is manually rotated over 180xc2x0 and placed on top of a stack of boxes previously formed.
2. The boxes fall on a catchment plate and form a stack. This plate is fitted longitudinally in the centre of a drum, the stack stays still and the drum rotates through 180xc2x0 about its longitudinal axis so that the lower edge of the catchment plate is now on the top. The following stack-forming series of boxes falls onto this. A pusher on the side edge presses the two stacks out of the drum simultaneously so that they fall onto each other and together form a compensated packet.
3. A type of carousel turns in the horizontal plane (like a merry-go-round). On four sides (2 by 2 opposite each other) arms are attached on the outside. On these arms is mounted a finger system, between which a stack can be clamped. The stack is held firmly on two opposing sides by the finger system. The held stack can be rotated about its horizontal axis through 180xc2x0. The carousel always turns 90xc2x0 further on each cycle, after two cycles the stack is again deposited and left. In this way unturned and turned stacks are placed on each other, thus forming a compensated packet.
4. A type of carousel turns in the vertical plane (like a windmill). On four sides (2 by 2 opposite each other) are attached arms at the outside. Attached to these arms is a clamping system. When a packet is pushed between these clamps (lying on one of the horizontal vanes) the carousel rotates through 90xc2x0 (vane is at the top). In this position the clamping system turns about its vertical axis. The carousel turns through a further 90xc2x0 (horizontal again) and pushes its load on top of an unturned stack already present.
Another embodiment of this turning in the vertical plane is described in U.S. Pat. No. 3,970,202, whereby two box receiving stations are located in vertically spaced planes. Means are provided for turning over a stack of folded boxes deposited in a first station and deposit it in a second station on top of a stack of flat-folded boxes already deposited there.
All these ways of compensating for non-planar stacks, show the disadvantage that compensation either takes a lot of time, or needs a lot of space.
Extra attention must furthermore be paid to the set-up problem. There is an increasing trend towards having less stock. This means that a manufacturer of cardboard boxes gets orders for smaller amounts of boxes to be supplied. As the manufacturer also wants to have a small stock, smaller production series must be made economic. Therefore, modern production machines have small set-up times and maximum output, and all this preferably automated. Manufacturers of folder-gluer machines have made advances towards handling of all kinds of boxes at very high speed. These folder-gluer machines can only have maximum efficiency if the subsequent machines, such as a packeting machine, can also handle the same kinds of boxes at the same high speeds.
It is an aim of the present invention to overcome the problems mentioned above, and to provide a machine which fulfils the market demands as fully as possible. In order to achieve this, the machine should preferably be able to process high throughputs very dynamically and to offer a very flexible system.
It is an aim of the present invention to meet one or more of the following requirements:
The system should be able to output one packet every 5 seconds.
The proposed dimensions are minimum 180 mmxc3x97180 mm and maximum 1400 mmxc3x971400 mm.
The system should be able to process the widest possible variety of product forms. This means that compensation of the packets must be possible.
Top- and under-stacking problems should also be handled.
The packets should be guided at all times to prevent unstable packets.
The manual settings should be reduced to a minimum and kept simple so that the total set-up time is always less than 10 minutes.
It is in particular an aim of the present invention to provide a method and a device for making stable packets of flat-folded boxes out of a continuous flow of flat-folded boxes in an overlapping shingled relationship, without stopping the continuous flow.
The above objectives are accomplished by a machine for production of a stack of stiff flat articles such as flat-folded boxes according to the present invention. The machine comprises an input device for feeding a horizontal flow of stiff flat articles, such as flat-folded boxes in an overlapping shingled relationship, a pusher mechanism for engaging with a side of one of the flat articles and for driving a plurality of flat articles into a vertical stack at a first location, and a transferring device for lifting the stack and transferring it to a second location. The transferring device is adapted to rotate the stack through a predetermined angle between lifting the stack at the first location and transferring it to the second location; preferably the rotation is done about a vertical axis.
According to the present invention, the movement of the pusher mechanism may be controlled in time and place, e.g. by software-based control system, by a hydraulic or pneumatic control system, or, for instance by a control actuator which may be manually operated. Preferably, a control device is provided, such as a computer, a PC, a PLC, an FPGA or any other suitable programmable control device. Preferably the pusher mechanism is actuated so as to make a movement towards the first location which is accelerated with regard to the movement of he horizontal flow of flat-folded boxes. Preferably, it receives a suitable signal or signals from the control device to control the time of starting, the rate of acceleration and when the acceleration should stop. The movement of the pusher mechanism may be controlled in its place or location or in its extent of movement in accordance with a dimension of the flat-folded boxes to be stacked, i.e. the thicker the flat-folded boxes to be stacked, the higher the pusher mechanism will move. This movement is done in accordance with suitable signals received from the control device.
The pusher mechanism may include a bottom-pusher mechanism, which is used in case of top-stacking of the flat-folded boxes, and/or a top-pusher mechanism, which is used in case of under-stacking of the flat-folded boxes. Preferably, both a bottom-pusher mechanism and a top-pusher mechanism are provided on one and the same machine, such that both kinds of shingled flows can be treated with the same machine.
Making a stack out of flat-folded boxes in an overlapping shingled relationship instead of first having to deliver the flat-folded boxes one by one, makes the handling thereof a lot faster compared to previously known machines.
A machine according to the present invention presents short simple set-up times with little but easily accessible safe controls. Flexible means processing of corrugated cardboard boxes in the broadest sense of the word: {fraction (4/6)}-point glued boxes are meant thereby, long seams and crash-lock bottom with widely varying dimensions and forms. Modularity is obtained by dividing the machine into three basic processing units.
The function cycle of the machine per station may be as follows:
The boxes are presented from the drying pressing belt of the folder-gluer to a packeting machine in shingled form. They are counted piece by piece and when reaching a preset quantity they are separated from the rest by an accelerated movement. The stack being formed comes to rest against a stop plate. The first part is called a counter packet collector.
In certain types of boxes a compensation is needed to achieve an easily processable bundle or packet. This is achieved by positioning a first layer (stack) and rotating a second or compensating layer (stack) through xe2x88x9290xc2x0, +90xe2x80x2 or 180xc2x0 before placing it on the first layer. This rotation/compensation system preferably comprises a four-axis portal robot with gripper arms.
Once the (compensated) bundle or packet is formed, it can be aligned in an output tunnel. The output tunnel consists of a set of side plates and pushers which move the packet and position it e.g. in a subsequent strapping machine.
The present invention also includes a method for production of a stack of stiff flat articles such as flat-folded boxes, which method comprises the following steps: feeding of a horizontal flow of flat articles in an overlapping shingled relationship; forming of a first stack from a plurality of flat articles at a first location; lifting of the stack and transfer of this to a second location, whereby the stack optionally is rotated through a predetermined angle about a vertical axis between the lifting of the stack at the first location and its transfer to the second location.
The present invention may also provide a counting system for counting flat articles moving in a continuous shingled stream, the system comprising: a fixedly mounted guiding element (23a) with a runner (23b) for running up the moving shingled stream of flat articles (90), and a rotation encoder connected to the runner.
Other characteristics and advantages of the invention may be seen from the following description of a specific embodiment of the method and installation for stacking flat-folded boxes according to the invention; this description is given for the sake of example only, without limiting the scope of the invention. The reference figures quoted below refer to the attached drawings.